Shift+Select a edges of a mesh after applying array modifier
If you hadn't enabled the Merge option in the Array Modifier, although they are in a single object, each duplicate of the mesh created by the array will be separate. To be able to select the entire line of edges, they need to be a single mesh. To join them, select all with A &gt; press M to merge &gt; click on By Distance. This will merge all the duplicate vertices together, giving you one single, continuous mesh. You can also specify a distance threshold.